Sergeant Andrew Savage, of the commercial vehicle investigation unit, said the incident happened as the truck and unladen semi-trailer turned over the bridge towards Anzac Ave, minutes after leaving a wharf-based depot.

The trailer became disconnected from the truck, coming to a rest on a crash rail.

No-one was injured in the incident, with the barrier sustaining some damage, he said.

The truck and trailer was now in storage to determine whether it was a mechanical issue or human error.